Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to electronic article surveillance (EAS) antennas, and more particularly to EAS antennas using multiple loop coils having at least one overlapping section.
2. Description of the Related Art
In the high fashion retail marketplace, retailers have a strong preference for discreet electronic article system protection. In locations where electronic article surveillance antennas are required and must be visible to pedestrian traffic, it is advantageous to design the antennas to be as transparent as possible. Near transparency is achievable by developing xe2x80x9clow visual massxe2x80x9d antennas, where the individual structural elements of the antenna are made as thin and sleek as possible. Having near transparent designs is a key market advantage in the high-end retail market.
Magnetomechanical EAS antennas can consist of one or more loops of coil wire adapted to transmit and receive preselected EAS frequencies. To optimize the detection performance of magnetomechanical EAS antennas, two coils are utilized, where the phase of each coil in the pair is reversed periodically during transmission, and the coil pairs overlap near the center of the antenna. Using conventional coil winding techniques, each antenna coil has a uniform cross-section, defined by the number of wire turns per layer multiplied by the number of layers. Given a uniform cross section for each antenna coil, the overlapping coils essentially double the thickness of the antenna at the cross-over point. An antenna with a thick center is undesirable for highly aesthetic, low visual mass antennas. A thin antenna with uniform antenna thickness along the antenna height is preferable.
An EAS antenna having uniform antenna thickness along the antenna height can be achieved if the individual coil cross-sections are variable with respect to the circumference. If the individual coil thickness is halved at the overlap, the antenna will have uniform thickness along the antenna height. This is accomplished by reducing the number of wire turns per layer along one or more sections of the coil, and simultaneously increasing the number of wire layers on the same sections.
In a first aspect of the invention, an electronic article surveillance antenna has a coil loop defined by a plurality of windings of a wire forming a loop. The coil loop has a first end and a second end, where a cross-section of the coil loop varies from the first end to the second end. The cross-section is defined by the number of windings of wire per a layer of the coil and the number of the layers per end.
The antenna can further include a second coil loop defined by a second plurality of windings of a second wire forming a second loop. The second coil loop has a first end and a second end, where a cross-section of the second coil loop varies from the first end to the second end. The cross-section of the second coil loop is defined by the number of windings of the second wire per a layer of the second coil and the number of the layers per end. The first ends of the first and the second coil loops are thinner than the second ends of the first and the second coil loops. The first and second coil loops are disposed in overlapping orientation with each other near the first ends, resulting in an antenna that is relatively uniform in thickness.
The first end of the first coil loop can consist of two windings of the first wire and eight layers, and the second end of the first coil loop can consist of four windings of the first wire and four layers. The first end of the second coil loop can consist of two windings of the second wire and eight layers, and the second end of the second coil loop can consist of four windings of the second wire and four layers.
In a second aspect of the invention, a method of winding a pair of overlapping coil loops to define an electronic article surveillance antenna having a substantially relatively uniform thickness dimension from end to end includes winding a first wire a plurality of windings to define a coil loop having a first end and a second end where the first end is thinner in cross-section that the second end. Then, winding a second wire a plurality of windings to define a second coil loop having a first end and a second end where the first end is thinner in cross-section that the second end. Finally, positioning the first coil loop and the second coil loop where the first ends overlap with each other forming an electronic article surveillance antenna with a substantially relatively uniform thickness.
Winding the first wire to form the first end to consist of two windings and eight layers of the first wire, and the second end to consist of four windings and four layers of the first wire. And, winding the second wire to form the first end to consist of two windings and eight layers of the second wire, and the second end to consist of four windings and four layers of the second wire.
Objectives, advantages, and applications of the present invention will be made apparent by the following detailed description of embodiments of the invention.